The present invention relates generally to processes for blow-molding and to articles made by blow-molding. More particularly, the present invention relates to multi-layer blow-molded bumper structures that incorporate reinforcing materials.
State-of-the-art automobile bumpers are typically manufactured by molding thermoplastics using a variety of molding techniques. These techniques strive to provide the best aesthetic qualities and structural strength, while reducing the material costs and weight of the finished product. Many techniques and bumper structures utilize reinforcing materials, such as glass fibers in order to increase the structural strength and reduce weight. While the use of such reinforcing materials is known to provide many desirable characteristics to molded articles, the use of such reinforcing materials in bumper structures produced by blow-molding techniques has heretofore been problematic. One reason for this is that the use of reinforcing materials in blow-molded bumper structures may produce irregularities or read-through in the outer surface finish of the bumper. Another reason is that the presence of many conventional reinforcing materials such as fiber reinforcement may render the bumper surface finish brittle and therefore unable to resist cracking when the bumper is subject to mild deformations.
In addition to the use of reinforcing materials, another known technique for increasing the strength of bumper structures involves the use of tacked-off bumper structures. In such structures, the internal surfaces of a bumper are made to contact and bond with each other to add structural strength. Typically, however, tacked-off structures result in a thermal sink and read-through to the finished surface. As such, tacked off structures have heretofore required the addition of a separately molded cover to provide an aesthetically pleasing exterior surface.
It would be desirable to provide blow-molded bumper structures which addresses the aforementioned shortcomings in the prior art. Specifically, it would be desirable to provide blow-molded bumper structures that utilize reinforcing materials, such as glass, mineral or carbon fibers or glass microspheres or nano-particles and which exhibit suitable surface finishes, even in bumper structures that incorporate tacked-off structures.
The aforementioned problems are eliminated and the desired advantages are realized by the present invention, which provides a blow-molded bumper structure that incorporates one or more internal layers that are reinforced with reinforcing materials, such as glass, mineral or carbon fibers or glass microspheres or nano-particles. The reinforced layer increases the strength of the bumper while reducing weight, density and material costs. The reinforced layer also provides a thermal barrier that acts to prevent read-through in tacked-off structures.
In one aspect, the invention may be defined as a blow-molded bumper including at least one inner layer containing a reinforcing material. More particularly, the invention may be defined as the aforementioned blow-molded bumper, wherein the reinforced layer is provided with glass fibers, mineral fibers, carbon fibers or glass microspheres or nano-particles.
In another aspect, the invention may be defined as a multi-layer blow-molded automobile bumper that includes at least one reinforced layer sandwiched between two unreinforced layers. More particularly, the invention may be defined as the aforementioned bumper, wherein the reinforced layer is provided with glass fibers, ceramic microspheres, mineral fibers, carbon fibers or glass microspheres or nano-particles.